Wireless communications technologies (WCT) are now expected to play a more significant role in underground mines as operators adjust to the complexities involved with the implementation of automation and management of digital data in harsh environments.
Up until now, the successful use of WCT in the deeps has faced a number of difficulties, including the shielding of signals due to rock masses, macroscopic geometry and the fact extractive activities generally take place in confined spaces.
Surrounding masses of varying materials — which are often supported by steel or wooden installations — are less penetrative for electromagnetic waves of wireless technologies.
Overall, these hinder the transmission of broadcasts significantly and result in a different signal attenuation when considering various scenarios.
Furthermore, alongside these installed signal blockages, the angle (in radians) about a vertical axis, the transversal positions of the antenna as well as fortifications in the form of pillars, metal and wooden installations.
“When going beyond the transmission of signals within the environment, local environment characteristics inherent to the mining operations need to be considered,” they noted.
“These determine requirements for the actual physical setup and maintenance of a network and its components and the possible usage, which is highly dependent on the setup within the environment.
“Mining environments do have an enormous variety depending on the naturally formed ore body and its properties that determine the mining method and used equipment.”
Moreover, in underground situations, the range of wireless technologies was highly dependent on specific conditions and significantly reduced for all technologies.
The high signal attenuation underground thus caused WCTs to become more dependent on line-of-sight (LOS) conditions.
Under this scenario, the further a signal had to travel, and the more obstacles it was required to pass, the more it was influenced by the conditions and dependent on propagation properties.
This dependency was stronger at higher frequency bands, making technologies in the “cellular” and high-frequency technologies in the “short-range” cluster decrease in range even more in an underground environment.
Low power wide area network (LPWAN) technologies, which operate at lower frequency bands, have a weaker LOS dependency and still result in a decrease in range underground.
In the case of such a transfer, the question of the timeliness of the technology itself for an underground application must be raised.
If a technology fulfilled the requirements of a use case, its timeliness was linked to the persistence of the use case itself. Nonetheless, the possibility for a network to be expanded, updated or modified still stood with new use cases.
“Underground monitoring applications, such as the Internet of Things sensor networks, are characterised by low power consumption and long range,” they said.
“LPWAN technologies meet these requirements, but the wireless technologies are also characterised by a low data rate.
“(Additionally) LPWAN applications can be found in many fields, such as asset tracking, smart city applications, smart metering and smart agriculture.
“In the mining sector, LPWAN technologies have great potential due to the increased need for connectivity and the potential of an increased range in underground spaces compared to existing technologies.
“These properties could enable data transmission with sparse installations in dynamic and widespread areas. Research underground is limited, but first investigations and tests show a promising application in the underground area.”
Use case examples were ubiquitous with coverage for safety, transmission of health/process status and/or position of worker mobile equipment, environmental monitoring of rock stress, gas concentration, asset tracking and predictive maintenance.
The network types use cases and resulting requirements were now directly connected to technologies, the researchers said.
“These can now be mapped onto the data rate and range space, which to some extent also aligns with acceptable cost and the ability to adapt to changing environmental conditions,” they noted.
“Each axis has a gap between the technologies. The most notable gap … shows that there is no technology that offers both a high data rate and a high range — this is due to the lack of penetration.
“According to the requirements from the use cases, automation and teleoperation networks can serve digitalisation applications, while tracking and tracing as well as long-range underground monitoring technologies can offer lower data rate connectivity at potentially lower costs and with less infrastructure installation, making them suitable for a wider range of applications.
“Each network type connected to technologies creates a space supporting the different use cases.”
Use case examples were ubiquitous with coverage for safety, transmission of health/process status and/or position of worker mobile equipment, environmental monitoring of rock stress, gas concentration, asset tracking and predictive maintenance.
The network types use cases and resulting requirements were now directly connected to technologies, the researchers said.
“These can now be mapped onto the data rate and range space, which to some extent also aligns with acceptable cost and the ability to adapt to changing environmental conditions,” they noted.
“Each axis has a gap between the technologies. The most notable gap … shows that there is no technology that offers both a high data rate and a high range — this is due to the lack of penetration.
“According to the requirements from the use cases, automation and teleoperation networks can serve digitalisation applications, while tracking and tracing as well as long-range underground monitoring technologies can offer lower data rate connectivity at potentially lower costs and with less infrastructure installation, making them suitable for a wider range of applications.
“Each network type connected to technologies creates a space supporting the different use cases.”